Recently, techniques for predicting safe routes to avoid collisions between moving bodies have been required in various fields including vehicle driving support systems and air traffic controls. With respect to vehicle driving support systems, for example, such a technique is developed that acquires positions of obstacles, such as vehicles and still objects around a host vehicle, by sensors installed in the host vehicle such as a millimeter wave radar, a laser radar, and a camera, determines collision risks from relative distances and relative speeds between the host vehicle and the obstacles, and then controls the host vehicle to prevent collisions. Further, as a more advanced technique, an automatic driving technique is being developed that recognizes surrounding environment by such sensors, automatically operates a steering wheel, a brake, or the like, without driver's operation, to reach the destination.
Patent document 1 discloses a method of generating routes and evaluating control variables of the host vehicle in consideration of interaction between plural vehicles. However, because the optimum predicted route is calculated on the basis of predetermined control rules, if there is a surrounding vehicle that does not follow the predetermined control rules, the predicated route may be erroneous. In addition, because sensor errors are not considered when positions of surrounding vehicles are observed, if the sensor errors are influential, the predicted route may be erroneous. Furthermore, there are many parameters to be set, such as a predicted speed of each of the surrounding vehicles given as a parameter; this leads to a concern that the design is complicated.
Patent document 2 discloses a method where plural predicted routes of vehicles are generated in advance, with respect to the generated predicted routes, degrees of interference of the predicted routes between the host vehicle and each of the surrounding vehicles are calculated, and thereby the route that best meets a predetermined selection criterion is selected. However, when calculating predicted routes of all surrounding vehicles, it is necessary to calculate the degree of interference for one predicted route of a surrounding vehicle considering all predicted routes of the other surrounding vehicles; this leads to a concern that the calculation load may be enormous. Further, only a method of calculating predicted routes of the host vehicle is disclosed, while no method of calculating the predicted routes of the surrounding vehicles is disclosed or suggested.
A more specific description will be given of the problem in calculating a predicted route under the circumstances where plural surrounding vehicles are in proximity. As illustrated in FIG. 11, it is assumed that vehicles E and D collide with preceding vehicles C and B, respectively. It is also assumed that the vehicle E has a high probability of moving to the right lane by steering to avoid the collision with the vehicle C, while the vehicle D, having no space on the left lane to move to, has a high probability of avoiding the collision by braking. However, as illustrated in FIG. 12, if the routes are predicted where the vehicle E steers and the vehicle D brakes to avoid the collision with respective preceding vehicles, possibility of collision between the vehicle D and the vehicle E arises. In this case, even if the collision between the vehicles D and E is avoided by re-prediction, another collision possibility arises, so that no predicted route that avoids all possible collisions can be calculated.